This invention relates to a resin composition comprising a polyamide resin, a polyphenylene ether resin, a block copolymer and .alpha., .beta.-unsaturated dicarboxylic acid or a derivative thereof, more particularly to a resin composition having excellent impact strength, and excellent balance in heat-resisting rigidity, heat-resisting aging property and molding property, and also available as a material for injection molding, extrusion molding and blow molding such as a member in the fields of automobile, electric and electronic.
Polyamide resin has widely been used as one of the representative engineering plastics excellent in heat resistance, oil resistance and molding property. However, this resin has defects that characteristics of dimensional stability, hygroscopicity, heat-resisting deformation property under high load and impact resistance are poor.
On the other hand, polyphenylene ether resin has been admitted as engineering plastics having excellent heat resistance, dimensional stability, non-hygroscopicity and electric characteristics, but there are defects that melt flowability is bad, working by molding is difficult and oil resistance and impact resistance are poor.
Thus, in order to provide a molding material without impairing merits of both materials and complementing each defects, various compositions have been proposed. For example, compositions wherein both of the resins are simply melted and mixed are disclosed in U.S. Pat. Nos. 3,379,792 and 4,338,421 and Japanese Patent Publications No. 997/1970 and No. 41663/1984. However, the polyamide resin and the polyphenylene ether resin are inherently bad in compatibility and thus, in such simple blended systems, affinity at the interface is poor and phase separation is caused at molding so that a composition excellent in mechanical strength cannot be obtained.
Accordingly, some methods for improving compatibility of the polyamide resin and the polyphenylene ether resin have been proposed. For example, a method in which a compound having a carbon-carbon double bond and a functional group such as a carboxyl group, acid anhydride group, acidamide group and imide group is added as a third component (Japanese Provisional Patent Publication No. 26913/1981), and a method in which a copolymer of styrene type compound and an .alpha., .beta.-unsaturated dicarboxylic acid is blended (Japanese Patent Publication No. 33614/1984). However, impact resistance is still insufficient even in these compositions, so that further improvement has been desired.
In order to improve impact resistance of a multiple-component polymer blended material such as a polyamide resin and a polyphenylene ether resin, it has been considered to mix and disperse an elastomer which is an improver for impact strength. Further, such a multiple-component material containing mutually incompatible components causes phase separation so that various characteristics have been considered to be greatly depending upon phase separation structure.
For example, there has been proposed in Japanese Provisional Patent Publication No. 27254/1987, a multi-phase structural material that, in a three-component system material comprising a polyamide resin, a polyphenylene ether resin and a specific A--B--A' type diene series block copolymer, when melting viscosities of the polyamide resin and the polyphenylene ether resin satisfy specific relationship, the polyamide resin exists as a continuous phase, the polyphenylene ether resin as a primary dispersed phase and the block copolymer as further secondary dispersed phase in the primary dispersed phase. According to the detailed description of the invention of the patent, there are described that composition ratio and viscosity ratio of the polyamide resin component and the polyphenylene ether resin component are important factors and selecting these suitably, the primary dispersed phase of the polyphenylene ether resin component is controlled in a suitable particle size range whereby properties such as impact strength and rigidity can be improved. However, it cannot be said that heat-resisting aging property, impact resistance and rigidity are sufficient.
Also, in Japanese Provisional Patent Publication No. 79258/1989, there is proposed a polyphenylene ether polyamide composition in which a hydrogenated block copolymer having a content of a vinyl aromatic compound and molecular weight in specific ranges is used as a third component. There are described that when this composition forms a specific multi-phase structure, i.e. the polyamide forms a continuous phase, the polyphenylene ether component exists as a dispersed phase having a specific grain diameter size and the block copolymer is being present with the secondary dispersed state in the polyphenylene ether dispersed phase, the product shows properties excellent in balance such as heat-resisting deformation, impact resistance, oil resistance and rigidity. However, impact resistance cannot yet be said to be sufficient.